www.it-ebooks.info C# 5.0 Pocket Reference C# is a general-purpose, type-safe, object-oriented programming language. The goal of the language is programmer productivity. To this end, the language balances simplicity, expressiveness, and performance. The C# language is platform-neutral, but it was written to work well with the Microsoft .NET Framework. C# 5.0 targets .NET Framework 4.5. The programs and code snippets in this book mirror those in Chapters 2-4 of C# 5.0 in a Nutshell and are all available as interactive samples in LINQPad. Working through these samples in conjunction with the book accelerates learning in that you can edit the samples and instantly see the results without needing to set up projects and solutions in Visual Studio. To download the samples, click the Samples tab in LINQPad and click “Download more samples”. LINQPad is free—go to www.linqpad.net. A First C# Program Here is a program that multiplies 12 by 30, and prints the result, 360, to the screen. The double forward slash indicates that the remainder of a line is a comment. using System; // Importing namespace class Test // Class declaration { static void Main() // Method declaration { int x = 12 * 30; // Statement 1 Console.WriteLine (x); // Statement 2 } // End of method } // End of class At the heart of this program lies two statements. Statements in C# execute sequentially and are terminated by a semicolon. The first statement computes the expression 12 * 30 and stores the result in a local variable, named x, which is an integer type. The second statement calls the Console class’s WriteLine method, to print the variable x to a text window on the screen. A method performs an action in a series of statements, called a statement block—a pair of braces containing zero or more statements. We defined a single method named Main. www.it-ebooks.info Writing higher-level functions that call upon lower-level functions simplifies a program. We can refactor our program with a reusable method that multiplies an integer by 12 as follows: using System; class Test { static void Main() { Console.WriteLine (FeetToInches (30)); // 360 Console.WriteLine (FeetToInches (100)); // 1200 } static int FeetToInches (int feet) { int inches = feet * 12; return inches; } } A method can receive input data from the caller by specifying parameters and output data back to the caller by specifying a return type. We defined a method called FeetToInches that has a parameter for inputting feet, and a return type for outputting inches, both of type int (integer). The literals 30 and 100 are the arguments passed to the FeetToInches method. The Main method in our example has empty parentheses because it has no parameters, and is void because it doesn’t return any value to its caller. C# recognizes a method called Main as signaling the default entry point of execution. The Main method may optionally return an integer (rather than void) in order to return a value to the execution environment. The Main method can also optionally accept an array of strings as a parameter (that will be populated with any arguments passed to the executable). For example: static int Main (string[] args) { } An array (such as string[]) represents a fixed number of elements of a particular type (see “Arrays”). Methods are one of several kinds of functions in C#. Another kind of function we used was the * operator, used to perform multiplication. There are also constructors, properties, events, indexers, and finalizers. In our example, the two methods are grouped into a class. A class groups function members and data members to form an object-oriented building block. The Console class groups members that handle command-line input/output functionality, such as the WriteLine method. Our Test class groups two methods—the Main method and the FeetToInches method. A class is a kind of type, which we will examine in “Type Basics”. At the outermost level of a program, types are organized into namespaces. The using directive was used to make the System namespace available to our application, to use the Console class. We could define all our classes within the TestPrograms namespace, as follows: www.it-ebooks.info using System; namespace TestPrograms { class Test { } class Test2 { } } The .NET Framework is organized into nested namespaces. For example, this is the namespace that contains types for handling text: using System.Text; The using directive is there for convenience; you can also refer to a type by its fully qualified name, which is the type name prefixed with its namespace, such as System.Text.StringBuilder. Compilation The C# compiler compiles source code, specified as a set of files with the .cs extension, into an assembly. An assembly is the unit of packaging and deployment in .NET. An assembly can be either an application or a library. A normal console or Windows ohas a Main method and is an .exe file. A library is a .dll and is equivalent to an .exe without an entry point. Its purpose is to be called upon (referenced) by an application or by other libraries. The .NET Framework is a set of libraries. The name of the C# compiler is csc.exe. You can either use an IDE such as Visual Studio to compile, or call csc manually from the command line. To compile manually, first save a program to a file such as MyFirstProgram.cs, and then go to the command line and invoke csc (located under %SystemRoot%\Microsoft.NET\Framework\<framework- version> where %SystemRoot% is your Windows directory) as follows: csc MyFirstProgram.cs This produces an application named MyFirstProgram.exe. To produce a library (.dll), do the following: csc /target:library MyFirstProgram.cs Syntax C# syntax is inspired by C and C++ syntax. In this section, we will describe C#’s elements of syntax, using the following program: using System; class Test { static void Main() { int x = 12 * 30; Console.WriteLine (x); } } www.it-ebooks.info Identifiers and Keywords Identifiers are names that programmers choose for their classes, methods, variables, and so on. These are the identifiers in our example program, in the order they appear: System Test Main x Console WriteLine An identifier must be a whole word, essentially made up of Unicode characters starting with a letter or underscore. C# identifiers are case-sensitive. By convention, parameters, local variables, and private fields should be in camel case (e.g., myVariable ), and all other identifiers should be in Pascal case (e.g., MyMethod ). Keywords are names reserved by the compiler that you can’t use as identifiers. These are the keywords in our example program: using class static void int Here is the full list of C# keywords: abstract as base bool break byte case catch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach goto if implicit in int interface internal is lock long namespace new null object operator out override params private protected public readonly ref return sbyte sealed short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushort using virtual void while Avoiding conflicts If you really want to use an identifier that clashes with a keyword, you can do so by qualifying it with the @ prefix. For instance: class class { } // Illegal class @class { } // Legal The @ symbol doesn’t form part of the identifier itself. So @myVariable is the same as myVariable. Contextual keywords Some keywords are contextual, meaning they can also be used as identifiers—without an @ symbol. These are: add ascending equals from join let set value www.it-ebooks.info async await by descending dynamic get global group in into on orderby partial remove select var where yield With contextual keywords, ambiguity cannot arise within the context in which they are used. Literals, Punctuators, and Operators Literals are primitive pieces of data lexically embedded into the program. The literals in our example program are 12 and 30. Punctuators help demarcate the structure of the program. The punctuators in our program are {, } and ;. The braces group multiple statements into a statement block. The semicolon terminates a (non-block) statement. Statements can wrap multiple lines: Console.WriteLine (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10); An operator transforms and combines expressions. Most operators in C# are denoted with a symbol, such as the multiplication operator, *. The operators in our program are: . () * = A period denotes a member of something (or a decimal point with numeric literals). Parentheses are used when declaring or calling a method; empty parentheses are used when the method accepts no arguments. The equals sign performs assignment (the double equals, ==, performs equality comparison). Comments C# offers two different styles of source-code documentation: single-line comments and multiline comments. A single-line comment begins with a double forward slash and continues until the end of the line. For example: int x = 3; // Comment about assigning 3 to x A multiline comment begins with /* and ends with */. For example: int x = 3; /* This is a comment that spans two lines */ Comments may embed XML documentation tags (see “XML Documentation”). Type Basics A type defines the blueprint for a value. . In our example, we used two literals of type int with values 12 and 30. We also declared a variable of type int whose name was x. A variable denotes a storage location that can contain different values over time. In contrast, a constant always represents the same value (more on this later). All values in C# are an instance of a specific type. The meaning of a value, and the set of possible values a variable can have, is determined by its type. www.it-ebooks.info Predefined Type Examples Predefined types (also called built-in types) are types that are specially supported by the compiler. The int type is a predefined type for representing the set of integers that fit into 32 bits of memory, from −2 31 to 2 31 −1. We can perform functions such as arithmetic with instances of the int type as follows: int x = 12 * 30; Another predefined C# type is string. The string type represents a sequence of characters, such as “.NET” or “http://oreilly.com”. We can work with strings by calling functions on them as follows: string message = "Hello world"; string upperMessage = message.ToUpper(); Console.WriteLine (upperMessage); // HELLO WORLD int x = 2012; message = message + x.ToString(); Console.WriteLine (message); // Hello world2012 The predefined bool type has exactly two possible values: true and false. The bool type is commonly used to conditionally branch execution flow with an if statement. For example: bool simpleVar = false; if (simpleVar) Console.WriteLine ("This will not print"); int x = 5000; bool lessThanAMile = x < 5280; if (lessThanAMile) Console.WriteLine ("This will print"); The System namespace in the .NET Framework contains many important types that are not predefined by C# (e.g., DateTime). Custom Type Examples Just as we can build complex functions from simple functions, we can build complex types from primitive types. In this example, we will define a custom type named UnitConverter—a class that serves as a blueprint for unit conversions: using System; public class UnitConverter { int ratio; // Field public UnitConverter (int unitRatio) // Constructor { ratio = unitRatio; } public int Convert (int unit) // Method { www.it-ebooks.info return unit * ratio; } } class Test { static void Main() { UnitConverter feetToInches = new UnitConverter(12); UnitConverter milesToFeet = new UnitConverter(5280); Console.Write (feetToInches.Convert(30)); // 360 Console.Write (feetToInches.Convert(100)); // 1200 Console.Write (feetToInches.Convert (milesToFeet.Convert(1))); // 63360 } } Members of a type A type contains data members and function members. The data member of UnitConverter is the field called ratio. The function members of UnitConverter are the Convert method and the UnitConverter’s constructor. Symmetry of predefined types and custom types A beautiful aspect of C# is that predefined types and custom types have few differences. The predefined int type serves as a blueprint for integers. It holds data—32 bits—and provides function members that use that data, such as ToString. Similarly, our custom UnitConverter type acts as a blueprint for unit conversions. It holds data—the ratio—and provides function members to use that data. Constructors and instantiation Data is created by instantiating a type. Predefined types can be instantiated simply by using a literal such as 12 or "Hello, world". The new operator creates instances of a custom type. We started our Main method by creating two instances of the UnitConverter type. Immediately after the new operator instantiates an object, the object’s constructor is called to perform initialization. A constructor is defined like a method, except that the method name and return type are reduced to the name of the enclosing type: public UnitConverter (int unitRatio) // Constructor { ratio = unitRatio; } Instance versus static members The data members and function members that operate on the instance of the type are called instance members. The UnitConverter’s Convert method and the int’s ToString method are examples of instance members. By default, members are instance members. Data members and function members that don’t operate on the instance of the type, but rather on the type itself, must be marked as static. The Test.Main and www.it-ebooks.info Console.WriteLine methods are static methods. The Console class is actually a static class, which means all its members are static. You never actually create instances of a Console—one console is shared across the whole application. To contrast instance versus static members, the instance field Name pertains to an instance of a particular Panda, whereas Population pertains to the set of all Panda instances: public class Panda { public string Name; // Instance field public static int Population; // Static field public Panda (string n) // Constructor { Name = n; // Assign instance field Population = Population+1; // Increment static field } } The following code creates two instances of the Panda, prints their names, and then prints the total population: Panda p1 = new Panda ("Pan Dee"); Panda p2 = new Panda ("Pan Dah"); Console.WriteLine (p1.Name); // Pan Dee Console.WriteLine (p2.Name); // Pan Dah Console.WriteLine (Panda.Population); // 2 The public keyword The public keyword exposes members to other classes. In this example, if the Name field in Panda was not public, the Test class could not access it. Marking a member public is how a type communicates: “Here is what I want other types to see— everything else is my own private implementation details.” In object-oriented terms, we say that the public members encapsulate the private members of the class. Conversions C# can convert between instances of compatible types. A conversion always creates a new value from an existing one. Conversions can be either implicit or explicit: implicit conversions happen automatically whereas explicit conversions require a cast. In the following example, we implicitly convert an int to a long type (which has twice the bitwise capacity of an int) and explicitly cast an int to a short type (which has half the bitwise capacity of an int): int x = 12345; // int is a 32-bit integer long y = x; // Implicit conversion to 64-bit int short z = (short)x; // Explicit conversion to 16-bit int In general, implicit conversions are allowed when the compiler can guarantee they will always succeed without loss of information. Otherwise, you must perform an explicit cast to convert between compatible types. www.it-ebooks.info Value Types Versus Reference Types C# types can be divided into value types and reference types. Value types comprise most built-in types (specifically, all numeric types, the char type, and the bool type) as well as custom struct and enum types. Reference types comprise all class, array, delegate, and interface types. The fundamental difference between value types and reference types is how they are handled in memory. Value types The content of a value type variable or constant is simply a value. For example, the content of the built-in value type, int, is 32 bits of data. You can define a custom value type with the struct keyword (see Figure 1): public struct Point { public int X, Y; } Figure 1. A value-type instance in memory The assignment of a value-type instance always copies the instance. For example: Point p1 = new Point(); p1.X = 7; Point p2 = p1; // Assignment causes copy Console.WriteLine (p1.X); // 7 Console.WriteLine (p2.X); // 7 p1.X = 9; // Change p1.X Console.WriteLine (p1.X); // 9 Console.WriteLine (p2.X); // 7 Figure 2 shows that p1 and p2 have independent storage. Figure 2. Assignment copies a value-type instance Reference types A reference type is more complex than a value type, having two parts: an object and the reference to that object. The content of a reference-type variable or constant is a reference to an object that contains the value. Here is the Point type from our previous example rewritten as a class (see Figure 3): www.it-ebooks.info [...]... Vertical tab 0x000B The \u (or \x) escape sequence lets you specify any Unicode character via its four-digit hexadecimal code char copyrightSymbol = '\u00A9'; char omegaSymbol = '\u03A9'; char newLine = '\u000A'; An implicit conversion from a char to a numeric type works for the numeric types that can accommodate an unsigned short For other numeric types, an explicit conversion is required String Type C# ’s... instance was declared as a field within an object, or as an array element, that instance lives on the heap You can’t explicitly delete objects in C# , as you can in C+ + An unreferenced object is eventually collected by the garbage collector The heap also stores static fields and constants Unlike objects allocated on the heap (which can get garbage-collected), these live until the application domain is... integral types checked can be used around either an expression or a statement block For example: int a = 1000000, b = 1000000; int c = checked (a * b); // Checks just the expression checked { c = a * b; } // Checks all expressions // in statement block You can make arithmetic overflow checking the default for all expressions in a program by compiling with the /checked+ command-line switch (in Visual... example: static int Max (int a, int b) { return (a > b) ? a : b; } The conditional operator is particularly useful in LINQ queries Strings and Characters C# ’s char type (aliasing the System.Char type) represents a Unicode character and occupies two bytes A char literal is specified inside single quotes: char c = 'A'; // Simple character www.it-ebooks.info Escape sequences express characters that cannot be... www.it-ebooks.info A constant declaration is like a variable declaration, except that it cannot be changed after it has been declared, and the initialization must occur with the declaration (more on this in “Constants”): const double c = 2.99792458E08; Local variable scope The scope of a local variable or local constant variable extends throughout the current block You cannot declare another local variable... Post-increment x++ Yes Post-decrement x Yes new Create instance new Foo() No stackalloc Unsafe stack allocation stackalloc(10) No www.it-ebooks.info typeof Get type from identifier typeof(int) No checked Integral overflow check on checked(x) No unchecked Integral overflow check off unchecked(x) No default Default value default(char) No await Await await mytask No sizeof Get size of struct sizeof(int) No + Positive... evaluated only once For instance: static void ShowCard (int cardNumber) { switch (cardNumber) { case 13: Console.WriteLine ("King"); break; case 12: Console.WriteLine ("Queen"); break; case 11: Console.WriteLine ("Jack"); break; default: // Any other cardNumber Console.WriteLine (cardNumber); break; } } You can only switch on an expression of a type that can be statically evaluated, which restricts it to... = p1; // Copies p1 reference Console.WriteLine (p1.X); Console.WriteLine (p2.X); // 7 // 7 p1.X = 9; Console.WriteLine (p1.X); Console.WriteLine (p2.X); // Change p1.X // 9 // 9 Figure 4 shows that p1 and p2 are two references that point to the same object Figure 4 Assignment copies a reference Null A reference can be assigned the literal null, indicating that the reference points to no object Assuming... Point is a class: Point p = null; Console.WriteLine (p == null); // True Accessing a member of a null reference generates a runtime error: Console.WriteLine (p.X); // NullReferenceException In contrast, a value type cannot ordinarily have a null value: www.it-ebooks.info struct Point { } Point p = null; // Compile-time error int x = null; // Compile-time error C# has a special construct called nullable... return x * Factorial (x-1); } This method is recursive, meaning that it calls itself Each time the method is entered, a new int is allocated on the stack, and each time the method exits, the int is deallocated Heap The heap is a block of memory in which objects (i.e., reference- type instances) reside Whenever a new object is created, it is allocated on the heap, and a reference to that object is returned . Backslash 0x 00 5C Null 0x 000 0 a Alert 0x 000 7  Backspace 0x 000 8 f Form feed 0x 00 0C New line 0x 000 A Carriage return 0x 000 D Horizontal tab 0x 000 9 v Vertical. Result ~ Complement ~0xfU 0xfffffff0U & And 0xf0 & 0x33 0x 30 www.it-ebooks.info | Or 0xf0 | 0x33 0xf3 ^ Exclusive Or 0xff 00 ^ 0x0ff0 0xf0f0 << Shift left 0x 20 <<. statement block. For example: int a = 100 000 0, b = 100 000 0; int c = checked (a * b); // Checks just the expression checked // Checks all expressions { // in statement block. c = a * b;